2000ApJ...531..820B

Frequency-switched observations of the 8.665 GHz hyperfine spin-flip transition of ³He⁺ have been made in eight Galactic H II regions in both the inner and outer Galaxy. For sources in the outer Galaxy, the observations reported here show no evidence for ³He⁺ to levels well below the level of detections claimed by Bania et al. using the position-switching technique. There is strong evidence that weak terrestrial interference is the explanation for the variability and relatively high level of ³He⁺ previously reported in several outer Galaxy sources. In the inner Galaxy, ³He⁺ is detected in W43, M17S, and W51 at abundance levels similar to those reported by Balser et al. with ³He⁺/H⁺~(1-2)x10^–5. Contrary to what has been reported previously, the ³He⁺/H⁺ abundances are found to decrease rapidly with increasing distance from the Galactic center and fall below detectable levels by the Galactic radius of W49 (∼8 kpc). This fall-off in ``second-generation'' ³He abundance with distance from the Galactic center is similar to what is predicted by the P_d=0 model of Galli et al. but is at least a factor of 5 underabundant. The upper limit to the antenna temperatures obtained here for the ³He⁺ lines in Orion A, W49, and S209 gives an upper limit for the abundance of primordial ³He that is an order of magnitude below the upper limit suggested by Bania et al. This leads to a lower limit for the nucleon-to-photon ratio η that is at least an order of magnitude above the narrow limits set by ⁷Li and deuterium. Possible explanations for this are that there is a larger than expected uncertainty in determining ³He abundances or that some mechanism is destroying primordial ³He in the Galaxy over a Hubble time.